Microfluidic devices may be used in a variety of biomedical and pharmaceutical applications, including analysis, preparation and synthesis of chemical compounds and analysis and manipulation of cells, proteins and nucleic acids. In many applications, the ability to concentrate or chromatographically separate compounds in a microfluidic environment enhances the utility of microfluidic devices. Thus, a rapid, inexpensive and effective method for performing chromatography and for microfluidic chromatography columns would be of great benefit. The present invention meets these and many other needs.